Difference scores between the % stability MAD of animals following acute saline when drug-naïve, or after prolonged administration of their assigned treatment. Abscissa: treatment group. Ordinate: Difference score measured as pre-treatment (drug-naïve) acute saline % stability MAD subtracted from the post-treatment (group assigned) acute saline % stability MAD. Significant differences were found between the MDPV and saline groups, but no differences were seen among either the MDPV and cocaine group, or the cocaine and saline group. *P < 0.05 compared to saline. MDPV, 3,4-methylenedioxypyrovalerone.